Cathode ray tube multiplex telephony system



Dec. 16, 1941.

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ffm/www1? M; x "5y 0% Patented Dec. 16, 1941 NT YOFFICE ACATHODE RAY TUBE MULTIPLEX TELEPHONY SYSTEM Menno Wolf, Eindhoven, Netherlands, vassignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as

trustee Application April 20, 1939, Serial No. 269,035 In Germany April 22, 1938 (Cl. Z50-152) 2 Claims.

My invention relates to multiplex telephony system-s employing cathode-ray tubes as the switching elements or current distributors.

In multiplex telephony systems it has been proposed to Vprovide cathode-ray tubes at the receiver and transmitter and to use the cathoderay beams thereof as switching members. For this purpose the cathode-ray beams are moved in synchronism along suitable stationary contacts each connected to a speech channel, and the transmission line between the transmitter and receiver is connected to elements of the tubes which always lie in the beams. It is the usual practice to arrange the stationary contacts of each tube in a circle and to employ a cathode-ray beam of small cross-section which is focussed by a radially-symmetrical electronic lens. By using suitable deflecting means this beam is moved with equal frequency and amplitudes in Itwo directions perpendicular to each other so that the beam describes a conical surface whose directrix is the circle upon which the stationary contacts are arranged.

One object of my invention is to improve and simplify the operation of such systems.

A further object is to increase the total current strength .of the tubes without increasing the electronic density.

A still further object is to simplify the deflecting means and the control thereof.

A further object is to prevent the cathoderay beam from transmitting current intoI the transmitting line during the time in which the beam passes between two successive stationary contacts.

Further objects and advantages of my inventicn will appear as the description progresses.

According to the invention, I use cathode-ray tubes having stationary Contact elements arranged side by side in a line and move the cathode-ray beam of each tube in only a single direction along this line. I prefer to use a tube having an electrode system which produces a cathode-ray beam having a band-shaped crosssection, and move this beam in the direction of its shorter cross-section dimension.

As stationary contacts for the cathode-ray tube at the receiver I may use a plurality of elongated impact electrodes extending throughout the length-.of the cross-section of the beam and each provided with a supply lead each adapted to be connected to one of the speech channels. In the cathode-ray tube at the transmitter the stationary contacts connected to the speech channels may be elongated control electrodes each provided with a supply lead and preferably extending throughout the length of the crosssection ,of the beam. In the latter case an impact electrode cooperating with all the control electrodes may be used to connect the transmission line to the movable circuit element, i. e. the cathode-ray beam.

To prevent the beam of rays from transmitting current into the transmission line during i the time in which it is located between two successive control electrodes, I prefer to provide the tube with a screen in the form of a `plate covering vthe intermediate spaces between the control electrodes and provided with apertures for the passage of the beam. These apertures are arranged .in accordance with the position of the stationary contacts, and the screen may be provided in front of these contacts, i. e. between the latter and the cathode.

The present invention has the advantage that the cathode-ray tube, which also serves as an amplifier, has a deflecting voltage-anode current characteristic curve of high slope and can operate with -high current strength. More particulary, as compared with the prior art, the cross-section of the beam is greatly increased in one direction and as a result the total current strength can be much higher without increasing theelectronic density. Furthermore, the synchronous movement of the beam along the stationary contacts can be effected in a very simple manner because the deecting means and .the control thereof have to deflect the beam in only a single direction.

In order that the invention may be clearly understood and readily carried into eect, I shall describe the same in more detail with reference to the accompanying drawing, in which,

Fig. 1 is a diagrammatic View of a portion of a multiplex system embodying the invention,

Fig. 2 is a plan View of an electrode system for use inthe tubes shown in Figure 1, and

Fig. 3 is a side view of Figure 2.

The multiplex system illustrated in Figure 1 has four transmitting channels ll, 4l, 42 and 43 connected to a transmitter, which in turn is connected through a common transmitting line L to a receiver connected to four receiving channels 50, 5I, 52 and 53. 'Io effect the switching two cathode-ray tubes 3i) and 2i! are provided at the transmitter and receiver respecltively.

The tube 3l! comprises a cathode 3i, a control electrode 34, two positive electrodes 32 and 33, and a single pair of deflecting plates 38 and 31. The electrodes are so constructed and arranged as to produce a band-shaped cathode-ray beam whose longer cross-sectional dimension is parallel to plates 36 and 31. The cathode-ray beam is reciprocated in the direction of the double-headed arrow, e. perpendicular to its longer cross-sectional dimension.

Tube 30 comprises as stationary circuit elements four control electrodes 35 each connected to one of the channels 1I, 4I, 42 and 43. As shown, each of the electrodes 35 is formed of two electrically-connected rods of conductive material which are spaced apart and extend parallel to each other throughout the length of the beam in a direction perpendicular to the direction of movement of the beam (indicated by the double-headed arrow). At the rear of electrodes 35 and common to the same is an anode 38 electrically connected to line L. As shown, anode 38 is in the form of a cylindrically-shaped sheet of metal. In front of electrodes 35 is a cylindrically-shaped screen 40, for instance of copper, which is provided with four slits 24, each located in front of one of the electrodes 35 and extending the length of the cathode-ray beam.

Tube 28, which is arranged at the receiver, isA

similar to tube 33 and has the same parts indicated by the same reference numerals. In this case, control electrode 34 is connected to line L, whereas in tube 36 the electrode 34 may be connected to cathode 3I through a source of constant biasing voltage (not shown). Tube 20 comprises four impact electrodes 25 each connected to one of the channels 5I) to 53. Electrodes 25, which are arranged side by side in the direction of movement of the beam, extend perpendicularly to the plane of the drawing and have a length at least that of the longer crosssectional dimension of the cathode-ray beam.

As stated, I use a band-shaped cathode-ray beam which can be produced in a manner known per se; for example by using a mirror-symmetrical electronic optical sytem, such as that illustrated diagrammatically in Figures 2 and 3. The system shown in these figures, comprises an incandescible cathode II, a focusing device I2, which during operation is preferably maintained slightly negative with respect to cathode II, a suction anode I3, an accelerating electrode I4 and a single pair of deflecting plates l5 and I6. The anode I3 and electrode I4 are given potentials which are different from each other and which are high and positive with respect to the voltage of the cathode; electrode I4 being of higher voltage than anode I3. The cathode II may be heated indirectly or directly and may be in the form of a rod, band or wire helix.

The electrode system of Figs. 2 and 3 produce a band-shaped cathode-ray beam 4 whose crosssection has a length q which is large compared l with its width p. For example, the length q may be about l mm. and the width p may be about l mm. The beam 4 is reciprocated by the deflecting eld in a direction perpendicular to the dimension q so that it impinges successively upon the stationary contacts (not shown), which, as stated above, are arranged side by side in the direction of movement oi the beam. Instead of using plates I5 and I6 to produce the deflecting eld, magnetic coils may be used in a manner well known in the art.

The deiiecting voltages applied to plates 36 and 31 of tube 30 is obtained from a suitable voltazcdevi age source 39, and this voltage is of the so-called saw-tooth type; i. e. a voltage which varies comparatively slowly from an initial value to a terminal value, during which the beam sweeps across the stationary contacts, and then returns quickly to the initial value.

This deflecting voltage is applied to plates 36 and 31 of tube 33 by a voltage-producing device 39, and to plates 36 and 31 of tube 20 by a voltage-producing device 29. Devices 29 and 39 produce a saw-tooth voltage and may be saw tooth generators of the type ordinarily used in cathode-ray oscillographs and in television receivers.

During operation the cathode-ray beam of tube 3U passes successively through the slotshaped apertures 24 and strikes the impact electrode 3S. At the same time the beam passes between the two rod-shaped portions of electrodes 35 and is modulated by the voltages applied to these electrodes by the speech channels 1I, 4I, 42 and 43; after which the anode current so modulated passes over the transmission line L to the receiver. After the cathode-ray beam has struck the impact electrode 38 through one end aperture 24 the beam returns quickly to the other end aperture and the procedure is repeated.

Deecting the cathode-ray beam by a sawtooth voltage has the advantage that with the symmetrical construction of the impact electrodes each of these electrodes is struck by the beam an equal number of times per time unit and each time during the same duration. This is favorable in connection with the quality of speech. As stated above, deflection may be produced by a magnetic field and in this case the magnetic coil or coils are connected to a source of saw-tooth voltage.

At the receiver a current successively modulated by the voltages produced in channels 1I, 4I, 42 and 43 and received via the transmission line L is supplied to the control electrode 34 so that the intensity of the cathode-ray beam of tube 2 is controlled successively and periodically in accordance with these voltages. The movement of the cathode-ray beam of tube 20 is in synchronism with the movement of the cathoderay of the tube 30, and during the time in which the beam is modulated, for example by the transmitting channel 1I, it strikes the impact electrode 25 connected to receiver channel 59. The transmission of the conversations from the sources of channels 4I, 42 and 43 to the channels 5I, 52 and 53 respectively, is brought about in a similar manner.

In tube 39 the plate 40, which comprises slotshaped apertures 24, covers the intermediate spaces between the control-electrode and thus makes it very easy to synchronize the device 29 with the device 39. More particularly, each time the cathode-ray beam of tube 30 strikes the plate 38 the current in the transmission line L is int-errupted, and it is only necessary that these interruptions of the current be derived by means of a lter 6I, for example an amplitude sieve, from the oscillations received via the said line and the device 29 be controlled in well-known manner by means of the pulsations occcurring in the output circuit of the said lter. Suitable means for synchronizing the beams of tubes 20 and 30 have been described, for instance in the U. S. Patent #1,779,748 to Nicolson.

I wish it to be understood that I do not desire to be limited to the exact details of construction 2. In a multiplex telephony system, a cathoderay tube serving as an interconnection switch at the transmitter and having an electrode system including a cathode, a plurality of stationary elongated control electrodes arranged side by side in a row, and a screen between said control electrodes and cathode and provided with apertures for the passage of the cathode-ray beam to said control electrodes, and means including said electrode system to produce a band-shaped cathoderay beam, each of said control electrodes and apertures having a length at least equal to the longer cross-sectional dimension of the beam.

MENNO WOLF. 

